PoSA

You'd think that, but all new (and some older) light rail systems are being outfitted with ATC outside of street operation. It reduces the requisite skill of the work force and proactively eliminates work to rule job actions as seen with the Boston light rail system.

Regarding Call-on signals (or PoSA signals as someone saw fit to rename them)

The interlocking covers as much as it can, leaving a little spare capacity in the case of SSI/Westlock/Smartlock where they're limited to 63 trackside modules.

RE interlockings, yes the US definition and the UK (+Europe+....) definition is very different. If you think of a simple single line with a passing loop ("siding" in US parlance), the Americans would stick two interlockings on that: one for each end of the loop. Each interlocking in this case would have a single point ("switch"and three signals (one coming off the signal line; two reading towards the single line). The interlocking limit is just the distance between the backs of the signals. Any automatic signals between interlockings are interlocked but not part of the interlocking ("go figure").

Interlockings in the UK (+Europe+...) don't have any relevance or meaning to drivers of trains - or even signallers generally. The above example would bundle probably a couple of those passing loops into a single interlocking, with the autos between as well. The interlocking covers as much as it can, leaving a little spare capacity in the case of SSI/Westlock/Smartlock where they're limited to 63 trackside modules.

" said:

Regarding Call-on signals (or PoSA signals as someone saw fit to rename them)

I think there's still a technical difference: I'm fairly sure PoSA consists of two white lights flashing, whereas standard call-ons are solid white.

" said:

The interlocking covers as much as it can, leaving a little spare capacity in the case of SSI/Westlock/Smartlock where they're limited to 63 trackside modules.

Out of interest, how much can a 'trackside module' consist of? What I mean is, does it include an entire signal (including route indicators etc.) or only parts? Would it be one per point end, or one per group of ends which always swing together, crossovers being the obvious example?

I think there's still a technical difference: I'm fairly sure PoSA consists of two white lights flashing, whereas standard call-ons are solid white.

RE interlockings, yes the US definition and the UK (+Europe+....) definition is very different. If you think of a simple single line with a passing loop ("siding" in US parlance), the Americans would stick two interlockings on that: one for each end of the loop.

Each interlocking in this case would have a single point ("switch"and three signals (one coming off the signal line; two reading towards the single line). The interlocking limit is just the distance between the backs of the signals. Any automatic signals between interlockings are interlocked but not part of the interlocking ("go figure").

Interlockings in the UK (+Europe+...) don't have any relevance or meaning to drivers of trains - or even signallers generally. The above example would bundle probably a couple of those passing loops into a single interlocking, with the autos between as well. The interlocking covers as much as it can, leaving a little spare capacity in the case of SSI/Westlock/Smartlock where they're limited to 63 trackside modules.

Broadly speaking, each module can handle one 4-aspect signal, two 3-aspect signals, or 2 points. I think the points modules can drive multiple ends but for detection purposes are normally split these days. Each module (whether point or signal) has 8 usable outputs and 8 usable inputs.

" said:

I think there's still a technical difference: I'm fairly sure PoSA consists of two white lights flashing, whereas standard call-ons are solid white.

Whoops, thanks for calling that to my attention. Can someone explain the rules difference between the two? Reminds me of the differences here between Restricting, Stop and Proceed and Restricted Proceed.

I was trying to keep it simple, Mike! There are always exceptions, especially where age of installation differs. There was the case of that Amtrak engineer getting confused between two aspects that were visually identical but meant very different things - on one journey, on two different railroads a few miles apart. Something NORAC and GCOR might have prevented but I guess nobody wanted to change "their" system to a standard one.

PoSA rules are available here. I can't seem to find the section of the rule book that formally defines the normal signal aspects though.

" said:

" said:

I think there's still a technical difference: I'm fairly sure PoSA consists of two white lights flashing, whereas standard call-ons are solid white.

Whoops, thanks for calling that to my attention. Can someone explain the rules difference between the two? Reminds me of the differences here between Restricting, Stop and Proceed and Restricted Proceed.

PoSA rules are available here. I can't seem to find the section of the rule book that formally defines the normal signal aspects though.

• Proceed to a siding


• Proceed for a shunt route


• Proceed to enter an occupied platform ("Calling-on")

" said:

I was trying to keep it simple, Mike! There are always exceptions, especially where age of installation differs. There was the case of that Amtrak engineer getting confused between two aspects that were visually identical but meant very different things - on one journey, on two different railroads a few miles apart. Something NORAC and GCOR might have prevented but I guess nobody wanted to change "their" system to a standard one.

Engineers, especially Amtrak engineers, need to be familiar with the operating rules they are working under.

In many cases the operating rules catered to ways that the railroads and signaling systems were constructed. Anyway, the confusion only resulted in a bit of a rear ender with a goods train resulting in no serious injuries.

" said:

PoSA rules are available here. I can't seem to find the section of the rule book that formally defines the normal signal aspects though.

Yeah, I read those rules and I wasn't sure how they could be markedly different from the steady on \ indication.

By "Engineers", are you using American vernacular as in "Train Driver" or the global term "Engineers" as in the overpaid ( :evil: ) professionals who design, install, commission and (to a lesser degree) maintain the signalling equipment?

The short and VERY generalised answer: PoSA (flashing white) is for working a train through a failed block section, shunt aspect (steady white) is for shunting (what you call "switching"). Trains may not enter an occupied section on a PoSA aspect. Trains most certainly ARE allowed to enter an occupied section on a shunt aspect.

Now, I'm answering this from the other side of the globe and stand to be corrected by my UK counterparts! But that's how it reads to me (plus a little operational knowledge).

9.2.13 RESTRICTING
Proceed at Restricted speed, not exceeding prescribed speed through turnout—when applicable.
Number Plate and Grade Plaque required, as shown.

6.27 Movement at Restricted Speed
When required to move at restricted speed, movement must be made at a speed that allows stopping within half the range of vision short of:
• Train.
• Engine.
• Railroad car.
• Men or equipment fouling the track.
• Stop signal.
or
• Derail or switch lined improperly.

When a train or engine is required to move at restricted speed, the crew must keep a lookout for broken rail and not exceed 20 MPH.

Comply with these requirements until the leading wheels reach a point where movement at restricted speed is no longer required.

" said:

The short and VERY generalised answer: PoSA (flashing white) is for working a train through a failed block section, shunt aspect (steady white) is for shunting (what you call "switching"). Trains may not enter an occupied section on a PoSA aspect. Trains most certainly ARE allowed to enter an occupied section on a shunt aspect.

Now, I'm answering this from the other side of the globe and stand to be corrected by my UK counterparts! But that's how it reads to me (plus a little operational knowledge).

Why is there a distinction there? A hazardous situation is a hazardous situation and trains should be operated in the same manner in both situations. .

What definition of "hazardous situation" are you using? Plenty of day-to-day railway tasks can be hazardous unless all the safety procedures are followed.

Entering an occupied section in day-to-day operation normally only happens when freight or empty passenger trains are sharing a line in a siding or yard, or passenger trains are sharing a line within designated platforms (not all stations allow this - The majority do not). These "normal" movements are controlled with standard subsidiary signals (constantly lit 2-diagonal-white-lights), all as part of the controlling signalling system.

POSA are only used for failures and disconnections. They *might* be used (can anyone confirm?) to allow an assisting train to access a failed train, but this would be in a location where two-in-a-section ("Permissive Working"is NOT allowed and the signaller wants the security of the route locking before allowing the movement to begin.

Remember, POSAs are still new the the UK railway. Before them, in any of failures I have mentioned in this and my previous posts, a signaller would have to manually set all the points and then authorise the train to pass the signal at danger. For this movement there is no route locking from the signalling system, and mistakes are *possible*. In areas with POSAs, these movements use the safety of the signalling system (interlocking) to set the route correctly and in a much more safe manner.

Engineers, especially Amtrak engineers, need to be familiar with the operating rules they are working under. In many cases the operating rules catered to ways that the railroads and signaling systems were constructed. Anyway, the confusion only resulted in a bit of a rear ender with a goods train resulting in no serious injuries.

" said:

Engineers, especially Amtrak engineers, need to be familiar with the operating rules they are working under. In many cases the operating rules catered to ways that the railroads and signaling systems were constructed. Anyway, the confusion only resulted in a bit of a rear ender with a goods train resulting in no serious injuries.

I think that neatly sums up the difference in our operating philosophies, don't you?

uses drivers that cannot be relied upon not to hit other trains

" said:

Engineers, especially Amtrak engineers, need to be familiar with the operating rules they are working under. In many cases the operating rules catered to ways that the railroads and signaling systems were constructed. Anyway, the confusion only resulted in a bit of a rear ender with a goods train resulting in no serious injuries.

I think that neatly sums up the difference in our operating philosophies, don't you?

I guess one "good" reason not to that I found while using SimSig is that it often screws up the train description system when I bunch a number of short trains into one block. Is that an accurate part of the simulation because that is a bit of a pain to deal with.

There hasn't been a similar incident since and crash resistant rolling stock, mitigated the accident.

Regarding permissive working, if drivers are relied upon to stop at bumper blocks other, non-train obstructions or employ it at station platforms, why not use it generally? Has there been a studying that calculated the number of accidents that might result from using PoSA to allow trains to bunch up?

I guess one "good" reason not to that I found while using SimSig is that it often screws up the train description system when I bunch a number of short trains into one block. Is that an accurate part of the simulation because that is a bit of a pain to deal with.

'Permissive block' used to exist back in steam and early diesel days, on goods lines only.

I guess one "good" reason not to that I found while using SimSig is that it often screws up the train description system when I bunch a number of short trains into one block. Is that an accurate part of the simulation because that is a bit of a pain to deal with.

" said:

'Permissive block' used to exist back in steam and early diesel days, on goods lines only.

There was also the working arrangements on the New Lines, correctly simulated in SimSig Euston. In the case of a failure this could result in several passenger trains waiting buffer-to-buffer.

" said:

" said:

'Permissive block' used to exist back in steam and early diesel days, on goods lines only.

There was also the working arrangements on the New Lines, correctly simulated in SimSig Euston. In the case of a failure this could result in several passenger trains waiting buffer-to-buffer.

I rather think this was an attempt to import US-style working into the UK, courtesy of Arthur Bound, the LMS CS&TE, who was strongly influenced by US practice.

The signalling installed on the 4th-rail electrified lines between Barking and Upminster was identical, I believe.

And London Transport - again influenced by US practice (courtesy of Yerkes' ownership of the early tube network) have always used stop & proceed working, with only local areas appearing on the diagrams in signal boxes. (Regulating Rooms invariably have a full display more akin to main line practice.) But it hasn't always worked well, with a number of unfortunate incidents marked up against it over the years.